First of all, the concept of the SCAT proposed by us is explained with reference to FIGS. 1A-1D.
The cordless electric tool such as an electric driver, an electric drill or an impact tool is constituted to include a motor for generating a rotating power by reducing the speed of the motor by a speed reducing mechanism and then transmitting the rotating power to a tip tool.
In FIG. 1A, numeral 20 designates a cordless electric tool, which is constituted to include a body trunk portion 20A and a handle portion 20B. A tool 30 is attached to the tip of the body trunk portion 20A. The handle portion 20B has its one end connected to the body trunk portion 20A and mounts a battery device 10 at its other end portion.
All these cordless electric tools are determined by the makers in the rated voltage (as will be abbreviated into “V”) and the current capacity (or the ampere time, as will be abbreviated into “Ah”). The rated voltage (V) is determined on the basis of both the magnitude of the rotating power to be transmitted to the tool and the voltage necessary for driving the motor for generating the rotating power. On the otherhand, the current capacity (Ah) is determined by both the magnitude of the load current of the motor and the specifications of the time period, for which the tool can be continuously used. For example, the electric tool having the battery device of 3 Ah mounted thereon is characterized to feed an electric current of 3 A continuously for one hour to the motor.
These rated voltage and current capacity are determined individually for every tools by the makers so that their values cannot be arbitrarily changed or modified by the users.
On the contrary, the SCAT proposes an electric tool of such a new concept that the current capacity (Ah) can be arbitrarily selected by the user although the rated voltage (V) of the electric tool is determined by the maker.
This new concept is desired in that one cordless electric tool can satisfy the various needs of the user. When the electric tool is used in a narrow place such as the ceiling space, for example, the user will desire the electric tool as light as possible better than the electric tool having a large current capacity. However, a half or so of the weight of the existing cordless electric tool is occupied by a battery pack or a battery device, and only the battery pack fitting the rated voltage and the current capacity of the electric tool can be mounted so that the weight of the electric tool cannot be changed for any operation.
In case it is desired to continue an operation for a long time, on the other hand, the desired electric tool can be used without its battery pack being frequently charged. However, the electric tool of the prior art is prefixed in the current capacity so that it cannot use battery packs of different current capacities for different operations.
The cordless electric tools of many kinds can naturally use tools of different situations for the different operations. However, the user will not desire to prepare many electric tools and to bring them to the working sites.
The SCAT can satisfy these various needs of the user. For example, the differences between the existing battery device and the battery device using the SCAT are described for the case, in which the electric tool has a rated voltage of 18 V and a current capacity of 3 Ah.
FIG. 1B shows the constitution of the battery device of the prior art of the case, in which a NiCd cell of a nominal voltage of 1.2 V is used as the battery dell. This battery device is constituted by connecting fifteen cells C1 to C15 in series and housing them in a battery pack container 10A.
In case the lithium cells are used as the battery cell, on the other hand, their nominal voltage is as high as 3.6 V, and the current capacity is so small as about 1.5 Ah. As shown in FIG. 1C, therefore, the battery device is constituted by connecting the series connection of the five cells C11 to C15 and the series connection of the five cells C21 to C25 in parallel and by housing the totally ten battery cells in the battery pack container 20A.
In the case of using the SCAT, on the contrary, the maker prepares the cell assembly, in which cells of the number needed for generating the rated voltage of the cordless electric tool are stored, as shown in FIG. 1D. In case the cell assembly is to be constituted by the lithium cells, for example, a cell assembly 100A is constituted by connecting five battery cells C11 to C15 having a nominal voltage of 3.6 V in series and by housing them in a container. Likewise, a cell assembly 100B is constituted by connecting the battery cells C21 to C25 in series and by housing them in the assembly container. These cell assemblies 100A, 100B, - - - , and 100N are so constituted that they may be connected, when stacked, in parallel.
The user can use one cell assembly as a battery device of 1.5 Ah, and can use two cell assemblies as a battery device of 3 Ah. In other words, the current capacity (Ah) of the cordless electric tool can be selectively determined by the user.
When the cell assembly is to be prepared by using the SCAT, it is desired to use the lithium cells having a high nominal voltage and a small current capacity. This is because the weight of the cell assembly can be reduced and because the current capacity can be finely selected by the user.
Here, the lithium cell indicates a vanadium-lithium cell, a manganese lithium cell or the like, which employs a lithium-aluminum alloy at its cathode and uses an organic electrolyte. On the other hand, the lithium ion cell generally employs cobaltous lithium in the anode and graphite in the cathode and uses an organic electrolyte as the electrolyte. Herein, for conveniences, the organic electrolyte secondary battery including the lithium cell and the lithium ion cell will be generally and merely called as the lithium cell.
As the prior art like the SCAT, there has already been proposed or developed the battery device, which is so constituted in the mobile electric device, e.g., a camera or a personal computer as ca connect a plurality of chargeable cells in parallel. For example, Patent Document 1 discloses a battery pack, which is used in a camera or the like and which can mount a desired number of auxiliary cells in addition to the main cell. In the case of the cordless electric tool, however, there exist technical problems of qualities different from those of the OA device or the mobile electronic device. Therefore, these problems have to be solved in case the battery device for the electric tool is developed by using the SCAT.
At first, one example of the cordless electric tool of the prior art is described with reference to FIG. 2A and FIG. 2B.
FIG. 2A shows the appearance of the cordless electric tool of the prior art, and FIG. 2B shows the electric circuit of the electric tool schematically. The electric tool 20 such as an electric driver, an electric drill or an electric wrench is constituted to include a body trunk portion 20A and a hand portion 20B connected to the body trunk portion 20A, and the battery device 10 is mounted on the end portion of the handle portion 20B.
In the housing of the body trunk portion 20A, there are housed a DC motor 210 for generating a rotating power, and a speed reducing mechanism portion 202 for reducing the rotating speed of the DC motor 201. A tip tool 30 such as a drill or a driver is attached to the tip of the speed reducing mechanism portion 202. In the case of the impact tool, an impact mechanism unit (although not shown) is interposed between the speed reducing mechanism portion 202 and the tip tool 30. Moreover, a trigger 203 is disposed near the connecting portion between body trunk portion 20A and the handle portion 20B.
As shown in FIG. 2B, a trigger switch 203A, the motor 201 and a switching element such as an FET are connected in series between the two terminals of the battery device 10. To the gate of the switching element 205, there is applied the pulse signal, which has its pulse width modulated by a control circuit 204. With this control circuit 204, there is connected a variable resistor 203B, which has its resistance varied in association with the operation of the trigger switch 203A. The pulse width of the output pulse of the control circuit 204 is varied by varying that resistance.
When the trigger 203 of FIG. 2A is pulled, the switch 203A of FIG. 2B is closed to apply the driving voltage is applied to the motor 201 by the battery device 10 only while the switching element 205 is ON, so that the motor 201 rotates. This rotating force is transmitted through the speed reducing mechanism 202 to the tip tool 30.
When the trigger 203 is pulled more deeply, the resistance of the variable resistor 203B varies. As a result, the pulse width of the pulses to be applied from the control circuit 204 to the gate of the switching element 205 is enlarged. As a result, the ON period of the switching element 205 is elongated to increase the average of the drive voltage to be applied to the motor 201. Thus, the rotating speed of the motor 201 can be controlled according to the pulling stroke of the trigger 203 thereby to control the magnitude of the rotating power to be transmitted to the tip tool 30. Moreover, the forward/backward rotating direction of the motor 201 can be switched by changing a switch 206 connected with the two ends of the motor 201.    [Patent Document 1] JP-A-2001-229891